I’d like to explore the prevailing belief that thicker plane blades are always superior to thinner ones. While it may seem like an intuitive truth, consider that the cantilevered portion of a bevel-down blade remains the same for thicker blades. It’s just moved farther away from the ramp on a larger, thicker cantilever. If the last fraction of an inch of the blade is flexing, adding to the thickness fails to modify the offending portion. That last, flexible fraction is still in play.There are some real advantages to thicker blades: when hollow ground, they are much easier to hold securely on a stone for honing — the edge and heel of the bevel register with positive, tactile feedback; many woodworkers like the feel of a plane with additional weight; and some additional mass and rigidity adds to the overall stability of the plane/blade system. But thicker for its own sake is overrated and may require modifications to the plane and breaker that are unnecessary. If the plane is properly fettled — the blade making good contact with the ramp, the cap iron* and lever cap both doing their jobs — a standard thickness blade will function as intended.
Thicker blades in bevel-up bench planes add needed support across the width of the mouth. The low bed angle employed in most bevel-up smoothers and jack planes creates a very thin wedge at the mouth that can be a bit fragile and a beefier iron helps that thin wedge resist deflection and possible fracture.
*While this may be a bit off topic, the illustration shows how a cap iron (chip breaker) contributes to a plane’s performance by adding pre-load stress and rigidity right down at the thinnest, most flexible part of the blade.
(The illustration is by Martha Garstang Hill from The Perfect Edge, the Ultimate Guide to Sharpening for Woodworkers.)